Known loop distribution systems (or access subnetworks) handle upstream and downstream data other than video data in a manner which is similar to that of a model Ethernet LAN. These known loop distribution systems are quite restrictive in either the manner in which non-video data is transported or in the type of non-video data which may be transported. As used in this application, the term "data" also includes control signals associated with a video connection or some other non-video application.
Typically, the downstream "data" is routed on a shared channel or other facility shared among a number of end users using IP packets ("IP" stands for Internet Protocol) and IP formatting. Each user on the network is assigned an "address" and a stream of IP packets containing data is forwarded to a particular user by attaching their address onto the stream of IP packets. However, the address is not used to direct the IP packets to particular equipment or to a particular physical destination. Rather, the stream of IP packets is made generally available on the network and users filter out the stream(s) of IP packets intended for them by using hardware or software which looks for their respective address.
The upstream "data" is typically routed using time division multiple access (TDMA) which assigns respectively different time slots for transmission to different users. Data for each user is sent upstream only during the timeslot assigned for that user. If necessary, packets of information from a single user can be distributed among successive timeslots assigned to that user. Once all of the upstream data gets into the shared channel or other shared facility of the distribution system, the origin of the packets of information can be identified from the time slots in which they are present and the information originating from one user can be reassembled by receiving equipment into its original form. The reassembled information can be distributed in the same manner as the downstream data using IP routing.
The Integrated Services Digital Network (ISDN) provides users with security and access to a 2B+D channel, in which each one of the two "B" channels guarantees 64 kilobits to the user whether they are using it or not. However, ISDN and IP are inflexible because they are reliant upon and restricted to a specific protocol, such as IP or ISDN.
Attempts have been made to improve the core switching, multiplexing and transmission technologies for integrated digital networks to support voice, data and video services from VIPs for multiple users. For example, fiber optic transmission systems with bandwidths ranging from 155.52 to 2,488.32 Mbps have been considered to improve bandwidth access. In addition, asynchronous transfer mode (ATM) has been developed as a technique to provide broad-bandwidth, low delay, packet-like switching and multiplexing in backbone networks. In ATM, usable capacity can be assigned dynamically (on demand) by allocating bandwidth capacity to supply fixed-sized information-bearing units called "cells" to point-to-point or multi-point outputs. Each cell contains header and information fields. The ATM standard, CCITT.121/2 specifies a 53 byte cell which includes a 5 byte header and a 48 byte payload.
However, customer premises equipment such as settop boxes generally cannot accept ATM and utilize an MPEG (moving picture experts group) standard for digital video program compression. A number of specific compression algorithms satisfy MPEG requirements. MPEG-2 is a second generation compression standard capable of encoding video program material into a 6 Mbits/sec bit stream and packetizing a number of 6 Mbits/sec channel streams into a single higher rate signal transport stream. The conversion of MPEG-2 data into ATM cell format, however, imposes additional overhead requirements that reduce the information-carrying capacity of the network. For example, synchronous transmission protocols, such as SONET, may require a stream of continuous data to retain synchronization. Thus, an ATM data stream carrying MPEG video data that is transmitted on a synchronous carrier may need to be padded with ATM idle cells, or "dummy cells", in order to ensure proper synchronization with the physical layer.
FIG. 1 depicts an example of a video network utilizing a hybrid fiber-coax system which provides RF transport of both analog and digital broadband services as well as a variety of data communications. The illustrated network provides broadcast video distribution, archival video services and interactive multi-media services as well as plain old telephone service. As discussed below, the data communications utilize IP addressing. To facilitate understanding, an overview of the network is given followed by a discussion of data transport through the network.
The network of FIG. 1 includes a Loop Transport Interface 10 located in a telco central office. In an area serviced through multiple central offices, several different central offices would each have a Loop Transport Interface similar in structure to the Interface 10 depicted in FIG. 1. In some respects, each Loop Transport Interface serves as the headend of an otherwise conventional optical fiber trunk and coaxial cable type CATV distribution network.
In the Loop Transport Interface 10, a laser type optical transmitter 12 transmits downstream signals through fibers 14 to optical to electrical nodes referred to as "optical network units" or ONU's. The laser operates in a linear mode in the range of 5-750 MHz. The transmitter 12 is followed by an optical splitter and can transmit to several ONU nodes 16. Each ONU 16 performs optical to electrical conversion on the downstream signals and supplies downstream RF electrical signals to a coaxial cable distribution system 18.
The optical transmitter receives and transmits signals from an RF (radio frequency) combiner 20. The combiner 20 combines levelized RF signals from several sources to produce the appropriate signal spectrum for driving the optical transmitter 12. One set of signals supplied to the RF combiner 20 are group of AM-VSB (amplitude modulated vestigial sideband) analog television signals 22 from one or more appropriate sources (not shown). Such signals are essentially "in-the-clear" CATV type broadcast signals capable of reception by any subscriber's cable ready television set. The analog television signals are broadcast from the optical transmitter 12 through the tree and branch optical and coax distribution network to provide "basic" CATV type service to all subscribers on the network. In order to obtain additional network services as discussed below, the subscriber may obtain a digital entertainment (DET) 24. A network interface module in the DET 24 includes a tuner that permits subscribers to the digital services to receive the analog broadcast channels through the same equipment used for the digital services. The network depicted in FIG. 1 also provides transport for digitized and compressed audio/video programming, both for certain broadcast services and for interactive services, such as video on demand. The network uses MPEG encoded video, which is transported to each Loop Transport Interface using asynchronous transfer mode (ATM) transport and switching. In the illustrated network, digital broadcast service signals 26 in MPEG encoded form and arranged in ATM cell packets are applied to an ATM packet demultiplexer 28 in the Loop Transport Interface 10. These broadcast service signals 26 originate in one or more broadcast VIP's ATM encoders controlled by the VIP servers. The ATM broadcast services carry premium service type programming. For certain interactive services which utilize one digitized channel to provide limited downstream transport to a large number of subscribers, the ATM broadcast cell stream signals originate from a server 30. Fully interactive broadband digital signals, in MPEG-ATM format, are also applied to the ATM packet demultiplexer 28 from an ATM switch 32. The ATM packet demultiplexer 28 terminates all ATM cell transport through the network, and converts the cell payload information into a plurality of MPEG-2 format bit streams.
In addition to the analog broadcast signals, the RF combiner 20 receives a variety of other analog RF signals from a group of RF digital modulators 34 that output the MPEG streams from the ATM packet demultiplexer 28 as digital broadband information in RF analog format. Each RF modulator 34 outputs a 6 MHz bandwidth IF signal which an upconverter (not shown) tunes to a different RF channel having a corresponding carrier frequency. A controller identified as the video manager 50 provides instructions to the ATM demultiplexer 28 to use the VPI/VCI header from the ATM cells to route the MPEG bit streams to the appropriate digital RF modulator 34. The video manager 50 provides the control information to the ATM packet demultiplexer 28, for example, by an ethernet bus 38a. The Ethernet bus 38a is also coupled to the network controller 36, the ACC 4000D 46, and the network data processor (NDP) 38. Thus, the video manager 50 and the ACC 4000 46 can provide control data for use by the ATM packet demultiplexer. The NDP 38 transmits downstream signaling and/or data via QPSK modulated out-of-band signaling channels. The network controller 36 receives and processes upstream signaling and/or data transmissions through upstream QPSK modulated out-of-band signaling channels.
The RF modulators 34 use 64 QAM (quadrature amplitude modulation) or 16 VSB (vestigial sideband) modulation techniques. The 64 QAM is used to modulate 4 channels of 6 Mbits/s MPEG encoded digital video information into one 6 MHz bandwidth analog channel. Similarly, 16 VSB modulates 6 channels of 6 Mbits/s MPEG encoded digital video information into one 6 MHz bandwidth analog channel.
As another example, U.S. Pat. No. 5,231,494 to Wachob, the disclosure of which is incorporated herein in its entirety by reference, teaches quadrature phase shift keyed (QPSK) modulation of a plurality of video, audio and data signals into a single data stream within a standard six MHz channel allocation for transmission over a CATV type distribution network.
The 6 MHz bandwidth RF signals from the modulators 34 are supplied to the optical transmitter 12 for downstream transmission together in a combined spectrum with the AM-VSB analog television signals 22. The downstream transport of the digital programming is an RF transmission essentially the same as for the analog basic service channels, but each of the channels from the RF modulators 34 contains 4 or 6 digitized and compressed video program channels, referred to hereinafter as "slots". The 6 Mhz digital program channels are carried through the fiber and coaxial system in standard CATV channels not used by the analog basic service programming. The ONU 16 is essentially transparent to both the analog basic service channels and the channels carrying the digital programming and supplies all of the signals as a combined broadcast over the coaxial cable network 18.
At the subscriber premises, a network interface module (NIM) (not shown) couples the set-top device or digital entertainment terminal (DET) 24 to a drop cable of the coaxial distribution network 18. In this network configuration, the NIM includes an analog frequency tuner controlled by a microprocessor to selectively receive the RF channel signals, including those channels carrying digital information. The NIM also includes a QPSK, QAM or VSB demodulator to demodulate a selected one of the digitized program signals carried in one of the digital slots within a received 6 MHz channel and performs a forward error correction function on the demodulated data. A digital audio/video signal processor within the DET decompresses received video signals, generates graphics display information and performs digital to analog conversion to produce output signals compatible with a conventional television set 40.
The analog tuner in the NIM tunes in all channel frequencies carried by the network, including those used for the analog broadcast services. The DET 24 includes a bypass switch in the NIM and an analog demodulator to selectively supply analog signals from the basic service channels directly to the audio/video output terminals or to the modulator, to provide signals to drive a standard television receiver.
The DET 24 also includes a remote control and/or keypad to receive various selection signals from a user. The DET relays data signals upstream over a QPSK signaling channel on the coaxial cable to the ONU 16 in response to user inputs such as selection of a pay per view event. The actual transmission of any such data signals upstream from the DET 24 occurs in response to a polling of the DET. The ONU 16 combines upstream data signals from the DET's serviced thereby and transmits those signals upstream over another optical fiber 42 to an optical receiver 44 in the Loop Transport Interface 10. Each DET 24 may transmit data on a different carrier frequency or timeslot, in which case the network controller 36 knows which DET sent particular data based on the received frequency channel. Alternatively, for interactive services, the DET may transmit a unique identification code with the upstream message.
In the implementation of the network illustrated in FIG. 1, an ACC 4000D 46 performs set top management and specific program access control functions. Service profiles for each customer on the network and their DET's are set up and stored within the ACC 4000D 46. The ACC 4000D 46 may also provide an interface to appropriate billing systems (not shown) for some broadcast services, such as pay per view. For ATM broadcast services, when a subscriber first signs up, a portfolio of channels subscribed to by that customer is established in the subscriber's profile data within the ACC 4000D 46. Based on this profile data, the ACC 4000D 46 downloads a service map into the subscriber's DET 24. The downstream transmission portion of the network provides an out-of-band downstream signalling channel to the DET's using internet protocol (IP) addressing. For example, for the downloading of the service map information from the ACC 4000D 46 to each DET 24, the ACC 4000D 46 outputs the service map information to the network data processor (NDP) 38 via the Ethernet 38a. The NDP includes a QPSK modulator for modulating the service map information onto the out-of-band downstream signaling channel. The modulated signals are then output to the RF combiner 20. At the subscriber site, the subscribers' DET/NIM would recognize, capture and process the out-of-band signaling data based on the corresponding IP address. This downstream signaling channel also carries signals for controlling software downloading and/or selection of certain channels or frames for decoding in interactive services.
All digital broadcast service signals are broadcast into each subscriber's premises, and each DET 24 includes means for receiving and decoding each such digital broadcast service channel, which may include premium channels. The microprocessor in the DET 24 controls access to any of these channels based on the downloaded map information stored in the system memory. For example, if one subscriber requests HBO, and that subscriber has paid to subscribe to HBO, the subscriber's DET 24 contains map information instructing it to tune to the RF channel and select and decode the digital program slot carrying HBO for display on the subscriber's television set 40. However, if a requesting subscriber has not paid for HBO, the downloaded service map will not provide the requisite data for tuning and decoding of that channel. If a decryption key is needed, the Level 1 Gateway 48 instructs the video manager 50 to instruct the ACC 4000D 46 to transmit the key to subscriber's DET 24.
The implementation of the network illustrated in FIG. 1 also provides telephone service. Between the optical network unit and the subscriber premises, the 700-750 MHz portion of the spectrum on the coaxial cable carries the telephone signals. This allocated spectrum provides transport for 24 DS0 telephone channels. Each subscriber premises has a telephone interface referred to as a Cable Network Unit (CNU) 52 coupled to the coaxial cable which serves to couple two-way signals between a twisted wire pair into the home and the telephone frequency channels on the coaxial cable 18. Upstream telephone signals are applied from the optical receiver 44 to a host digital terminal (HDT) 54 which provides an interface to a standard digital telephone switch 56. Downstream telephone signals from the switch 56 pass through the HDT 54 to the RF combiner 20 for transmission in the 700-750 MHz frequency range over the fiber to the ONU 16 and the coaxial cable distribution system 18. Upstream telephone signals are output in the 5-40 MHz frequency range of the coaxial cable, which are block converted in the fiber nodes for transport on an optical fiber.
The implementation of the network illustrated in FIG. 1 also offers access to video information providers (VIP's) for interactive broadband services, such as video on demand. For archival services and many other interactive services, each VIP has a level 2 gateway and some form of broadband information file server 403. The ATM switch 32 provides communications links between the Loop Transport Interfaces 10 and the level 2 gateways and file servers 60. Customer access to the VIP's is controlled through one or possibly more programmed computer or processor elements performing the processing functions of the Level 1 Gateway 48. A permanent virtual circuit (PVC) controller 56 and a video manager 50 respond to signals from the Level 1 Gateway to control the point to point routing through the network.
The PVC controller 56 stores data tables defining all possible virtual circuits through the ATM switch 32 and the Loop Transport Interface 10 serving each DET terminal of a customer subscribing to each particular provider's services. These data tables define the header information and the switch port to the packet handlers needed to route cells to the correct Loop Transport Interface. The video manager 50 stores similar data tables identifying the transmission fiber ports, RF channels and multiplexed digital channel slots which may be used to transport each data stream processed by the ATM packet demultiplexer 28 through the fiber 14 to the appropriate ONU 16 serving each DET. The data tables in the PVC controller 56 and the video manager 50 thus define "permanent virtual circuits" between the VIP's equipment 403 and the DET's 24.
For a full, broadband interactive session, the subscriber operates the DET 24 to interact with the Level 1 Gateway 48 and select a VIP. The PVC controller 56 responds to instructions from the Level 1 Gateway by activating the ATM switch 32 to establish a downstream virtual circuit path between a port of the VIP's server and the ATM packet demultiplexer 28 within the Loop Transport Interface 10 servicing a subscriber requesting a call connection to the particular VIP. The video manager 50 assigns a particular one of the digitized video channel slots in a digital program type RF channel to carry the particular point to point communication. Specifically, the video manager controls the ATM packet demultiplexer 28 to route MPEG data recovered from the ATM cells for the particular point to point communication to the port for one of the RF modulators 34 so that the modulator will include the MPEG data in the assigned digital channel slot within a particular 6 MHz RF channel. The video manager 50 also transmits a signal downstream through NDP 38 and the signaling channel to the subscriber's DET 24 instructing the DET to tune to the particular RF channel and decode MPEG data from the specifically assigned digital channel within that RF channel. Similar dynamic assignments of RF channels on a CATV system to individual terminals for interactive services are disclosed in U.S. Pat. No. 5,220,420 to Hoarty et al. and U.S. Pat. No. 5,136,411 to Paik et al., the disclosures of which are incorporated herein in the entirety by reference.
Concurrently, the Level 1 Gateway 48 would instruct the PVC controller 56 to control the ATM switch 32 to establish an upstream virtual circuit for control signals sent from the DET 24. In such a case, the upstream signals from the DET are passed up through the fiber-coax network and receiver 44 to the network controller 36, and then the VIP's level 2, gateway via the ATM switch 32.
The network disclosed in FIG. 1 has limited flexibility in that the ATM packet demultiplexer 28 recovers MPEG data having preassigned PID values from the ATM cell streams. It would be desirable to provide an ATM packet demultiplexer that provides additional flexibility in MPEG encoding to enable dynamic MPEG encoding of ATM cell streams.
The ATM packet demultiplexer 28 also is limited in that the ATM cell streams generally must include MPEG-encoded data streams before transmission through the network. Downstream signaling from the VIP's equipment to the DET therefore must be encapsulated as user data within MPEG packets, by an encoder operated by the VIP. It would be desirable to provide an arrangement that did not necessarily require MPEG-encoded data in the ATM cells transported to the loop transport interface 10, but that was adapted to accept ATM cells carrying different data formats.
As noted, the network disclosed in FIG. 1 involves IP addressing using TCP/IP protocol. This technique, however, results in additional IP address management at the VIP and each loop transport interface, as well as additional IP processing at the DET. It is anticipated that the increased popularity of Internet will result in revision in protocol standards to accommodate increased IP address lengths, thereby increasing overhead and reducing available bandwidth on the network for signaling and data transmission. Further, the network disclosed in FIG. 1 requires different data paths for video data and signaling data, thereby complicating data transport to the DET. It would be desirable to provide a more flexible, efficient signaling communication system that transports signaling information to individual DET's.
There are at least two main disadvantages to broadcast systems using IP addressing of non-video data messages. The first is security. When using IP packets and IP information in the manner described in the preceding paragraphs, the data is made available to each user and it is intended that each user will receive only the data which is intended for them. However, since the data is provided to each user, it is possible for the data to be obtained by a user other than the one to which the stream of IP packets was addressed by hacking of equipment or other means. Therefore, there is no easy and reliable way to provide private and secure communications with a single user.
Secondly, these systems suffer from diminished performance in their capacity to transport information from point to point because data is transferred to all points, and the time which it takes to do so necessarily depends upon the amount of overall traffic in the system.